It is known to provide thermally insulated vessels for low-boiling point liquids and especially liquefied gases such as liquefied natural gas, methane ammonia, nitrogen, oxygen, which consists of an inner receptacle containing the liquefied gas, frequently under pressure, and an outer vessel separated from the inner vessel by an insulation-filled and/or evacuated space.
Such vessels may be provided upon vehicles, ships or the like for the transportation of the liquefied gas or may be located at fixed sites for the storage of liquefied gas convenient to location at which a liquefied gas is produced or consumed.
The present invention relates primarily to storage or transport vessels in which the interwall space is evacuated, i.e. to so-called vacuum-insulated double wall vessels.
In vessels of the latter type the outer and inner receptacles are generally both made so as to be highly rigid and can bear upon one another with bearing elements capable of yielding or otherwise adapted to take up the changes in length of the receptacles with temperature fluctuations. The vessel may be subjected to large temperature variations, i.e. a temperature change between ambient and the boiling point of the liquefied gas, the temperature change is considerable.
The outer receptacle has, because of its rigid and massive configuration, considerable weight. This is a disadvantage when the vessel is to be used for the transport of liquefied gases since it reduces the payload which can be carried by the ship or vehicle. Even where the vessel is to be fixedly located, the massive character of the outer receptacle is a disadvantage because of the high material and construction costs.
It has been proposed to reduce the weight of the outer vessel by making the latter of a smaller wall thickness and stiffening it at selected locations with a plurality of stiffening rings. The disadvantage of this arrangement is that it requires considerable work and high labor costs.